The role of A species in vascular smooth muscle cell and cerebral arteriole dysfunction. Alzheimer's Disease (AD) is the leading cause of dementia; yet no therapy exists to slow or stop its progression. Recently, cerebrovascular (CV) pathology has been identified as a strong contributor to AD. Two key observations suggest that amyloid- peptide (A) may play a role by either causing or increasing the susceptibility to cerebral ischemia. First, cerebral blood flow (CBF) is reduced in early stages of AD, and the reactivity of cerebral blood vessels is impaired - both of which have been linked to the vasoactive properties of A. Second, most AD patients develop A deposits not only in brain but also in vessels - a condition known as cerebral amyloid angiopathy (CAA). CAA is a powerful risk factor for brain infarction and dementia, and is associated with severe CV dysfunction. A2 exists in several forms including soluble monomers (such as A40 and A42), soluble oligomers (toxic intermediate species), and insoluble fibrils (principle component of CAA). The former (primarily A40) and the latter (fibrillar A2 in the form of CAA) have been shown to powerfully alter CV function, while the vascular effects of A2 oligomers are not known. Our preliminary data suggest that the manner and extent to which monomeric A2 vs. fibrillar A2 cause CV dysfunction is different. We find that A monomers cause a hyper-contractile vascular phenotype that is due to endothelial cell (EC) and vascular smooth muscle cell (VSMC) dysfunction that is mediated via reactive oxygen species (ROS), while A fibrils in the form of CAA cause a hypo-contractile vascular phenotype that is primarily due to VSMC dysfunction that is mediated via ROS. We also identified a previously unrecognized contribution of ROS to CAA formation. The long-term objective of the proposed project is to test the central hypothesis that A species powerfully and adversely affect the cerebral circulation by inducing VSMC-mediated arteriole dysfunction via an ROS- mediated pathway. The specific aims are 1) to determine whether A species cause differential CV effects (hyper- vs. hypo-contractile impairment); 2) to determine the ROS pathways by which A species cause VSMC and cerebral arteriole dysfunction; and 3) to determine the manner and extent to which ROS contribute to CAA formation, and to assess the functional benefits of reducing CAA via anti-ROS strategies. Methods used will include a) in vitro assessment of VSMC function after application of exogenous A species; b) in vivo assessment of cerebral arteriole function in transgenic mice producing endogenous A species; c) immunotherapy with anti-A antibodies that bind A40, A42, A oligomers, and/or A fibrils; d) pharmacologic and genetic inhibition of NADPH oxidase; d) pharmacologic and genetic inhibition of the A2-binding cell surface receptors, LRP1 and HSPGs; and e) quantitation of CAA, A40, A42, APP, and ApoE. If successful, these studies will result in an improved understanding of the mechanisms underlying A-induced CV deficits and CAA formation. This will likely facilitate development of therapies targeting A and its downstream effectors, which may ultimately improve the outcome of patients with AD, CAA, or both.